Helicobacter pylori is a widely prevalent organism found on gastric biopsy in approximately 30% of the population less than 40 years old with increasing incidence thereafter. The organism is a causative agent of chronic gastritis in humans (e.g. Marshall & Warren, 1984*; Blaser, 1990*). Epidemiological studies have shown that H. pylori is most commonly found in association with gastritis. Serological investigations have demonstrated that evidence of a current or prior infection can be found in 30-50% of a randomly chosen population of blood donors. No direct causal relationship has been conclusively proven for duodenal ulcer disease. However, the organism is found in 95% of patients with duodenal ulcer. Further, eradication of the organism results in rapid ulcer healing (e.g. Rauws & Tytgat, 1990*). These data provide strong evidence that H. pylori is a dominant factor in the development of duodenal ulcer. Additional evidence for the pathogenic involvement of H. pylori in these conditions has been provided by studies with gnotobiotic piglets (Lambert et al., 1987*) and the fulfilment of Koch's postulates with human volunteers (Marshall et al., 1985*; Morris & Nicholson, 1987*/).
In addition, there is now strong circumstantial evidence implicating H. pylori in the pathogenesis of gastric carcinoma (e.g. Jiang et al., 1987*; Lambert et al, 1986*; Crabtree et al., 1992; 1993; Forman et al., 1990, 1991; Nomura et al, 1991; Parsonnet et al., 1991; Correa et al., 1990). Most recently, the Eurogast Study Group, led by Forman (1993), demonstrated a significant relationship between H. pylori seropositivity and gastric cancer mortality and incidence. Indeed, there is now a convincing body of literature implicating infection with H. pylori in a considerable proportion of upper gastrointestinal morbidity. A number of hypotheses have been suggested for the pathogenic mechanisms of H. pylori induced gastroduodenal disease, including the production of cytotoxins and mechanical disruption of the epithelium (e.g. Blaser, 1992*). Interestingly, however, many infected persons remain asymptomatic despite the persistent presence of the pathogen (Taylor & Blaser, 1991*).
Diagnosis of infections with H. pylori is based mainly on histology and culture from gastric biopsy specimens or on indirect methods based on urease activity. Various serological assays have been developed for the detection of anti-H. pylori antibodies in epidemiological studies in addition to more molecular oriented approaches such as the cloning of H. pylori species-specific antigens for use in, for example, PCR-based serological investigations (e.g. Clayton et al., 1989). However, the use of recombinant species-specific antigens has not yet received widespread use and, consequently, the majority of immunosorbent-based assays currently in use employ various subcellular fractions of H. pylori as a source of antigen. The fractions of proteins used in these assays are frequently heterogeneous in composition as are their methods of preparation. Interestingly, a number of groups have compared the inter-assay sensitivity and specificity of several commercially available ELISA kits manufactured specifically for serological studies. Not surprisingly, considerable inter-assay variation was observed. Caution, therefore, must be exercised before employing a particular preparation of protein for use in such immunosorbent assays, particularly in view of the significant genetic heterogeneity of different strains of H. pylori (e.g. Xia et al., 1994; Owen et al., 1991).
We have studied the prevalence of immuno-reactivity to H. pylori in both infected and uninfected individuals and found that un-infected individuals have a high response to H. pylori both in their B-cell and T-cell systems. In this approach, we use Western blotting to investigate antigen specificity of systemic responses to H. pylori in both healthy and H. pylori-infected individuals and show that the incidence of seropositivity in H. pylori negative individuals is much greater than has previously been demonstrated. Furthermore, we have demonstrated that antibodies to a 25 kDa protein are detectable in the majority of H. pylori negative individuals. These were detected using a technique which we have modified called Enhanced Chemiluminescence. Enhanced Chemiluminescence on Western blot analysis reveals that the majority of uninfected individuals have antibodies which are specific for H. pylori and recognize antigens which are not present on other microorganisms. Of these antigens, the most common one recognized is a 18-19 kDa protein which appears to be specific to H. pylori. Hence, these data suggest that immunization with the 18-19 kDa protein or sub-unit thereof could have the potential to confer protective immunity on individuals who are either uninfected with the organism or individuals in whom the organism has been cleared by anti-bacterial treatment. We have derived N-terminal and internal amino acid sequences from this protein.